This proposal is designed to test the hypothesis that (i) oxidants increase and antioxidants decrease the size and steroidogenic capability of the ovarian thecal-interstitial (T-I) compartment and (ii) insulin, insulin-like growth factor I (IGF- I) and tumor necrosis factor alpha (TNF-alpha) stimulate growth of T-I cells by inducing oxidative stress. We propose that, under pathological conditions, excessive oxidative stress on T-I cells may contribute to the development of polycystic ovary syndrome (PCOS). This hypothesis is based on evidence indicating that other disorders associated with insulin resistance and hyperinsulinemia, such as syndrome X, are characterized by increased oxidative stress and reduced radical-trapping, antioxidant capacity. We propose that insulin and insulin-like growth factors (IGFs) increase oxidative stress and thus cause relative depletion of antioxidants such as vitamin E. Conditions associated with hyperinsulinemia and/or increased bioavailable IGFs are also characterized by increased proliferation of several mesenchymal tissues including vascular smooth muscle and skin fibroblasts. Similarly, women with PCOS have insulin resistance, compensatory hyperinsulinemia, and increased levels of free IGF- I. Our studies have shown that insulin and IGFs promote proliferation and decrease apoptosis of T-I cells; these effects likely contribute to hyperplasia of T-I cells, a characteristic feature of PCOS. Our preliminary data demonstrate that in vitro administration of vitamin E succinate and other antioxidants inhibit proliferation of T-I cells in a dose-dependent fashion. In contrast, induction of modest oxidative stress stimulates proliferation. The specific aims of this proposal are: (i) to study the effects of oxidants and antioxidants on T-I proliferation, steroidogenesis, and apoptosis; and (ii) to evaluate the role of insulin, IGF-I and TNF-alpha in the generation of reactive oxygen species in cultures of T-I cells. These aims will be addressed by experiments on rat T-I cell cultures. The relevance of the key findings to the human ovary will be tested. The results of these studies will provide a new insight into the role of oxidative stress and antioxidants, especially vitamin E, on the growth and function of ovarian mesenchyme. Ultimately, this study may shed new light on the pathophysiology of PCOS and thus provide an impetus towards development of new diagnostic and therapeutic approaches, including the possible therapeutic use of antioxidants.